Apparatus and ejector for producing cold



1969 J. A. RIETDIJK 3,442,093

APPARATUS AND EJECTOR FOR PRODUCING COLD Filed June 26, 1967 Sheet 0r 2 Nil 1'7 FIG] n INVENTOR. JOHAN A.RIETDUK BY id 4% AG T May 969 J. A. RI ETDIJK 3,442,093 APPARATUS-AND EJECTOR FOR PRODUCING COLD Filed June 26, 1967 NVENTOR. JOHA" A.RIE K BY MK I AGEN Sheet 2, of

United States Patent 3,442,093 APPARATUS AND EJECTOR FOR PRODUCING COLD Johan Andriaan Rietdijk, Emmasingel, Eindhoi en, Netherlands, assignor, by mesne assignments, to US. Philips Corporation, a corporation of Delaware Filed June 26, 1967, Ser. No. 648,874 Claims priority, application Netherlands, July 1, 1966, 6609177 Int. Cl. F25b 23/00 US. Cl. 62500 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates to apparatus for producing cold wherein fluid medium from a high pressure source is: first cooled to its inversion temperature associated with that pressure, and then expanded in an ejector and discharged to a first reservoir with vapor therefrom returning to said source; subsequently medium from the reservoir is further expanded in a throttling device, and discharged to a second reservoir with vapor therefrom being pumped in the suction inlet of the ejector. The ejector has jet tube and diffuser portions through which the medium flows, and the area of the jet tube contacted by the medium or the whole jet tube is made of heat insulating material for preventing the conduction of heat through the walls of the jet tube toward the end thereof.

In known machines for producing cold and/or for liquefying gases, a flow of high-pressure medium is cooled in one or more heat-exchangers below the inversion temperature corresponding to the pressure of the medium, whereupon the medium is throttled to a considerably lower pressure in one or more Joule-Kelvin cocks. Wit-h suitable choice of the pressure and temperature, a fall in temperature of the medium or a phase transition of part of the medium or both will occur during the throttling process in the said Joule-Kelvin cocks. The medium of reduced pressure may then be brought into heat-exchange with an object or medium to be cooled. If phase transition has taken place the liquid produced may, if desired, be partly removed from the machine. The low-pressure vapour produced is then led off to the surroundings or back to a compressor providing the high pressure medium.

To obtain very low temperatures it is necessary to throttle to very low pressures. If, for example, the medium used is helium and cold is to be produced at a temperature of 42 Kelvin, it is necessary to throttle to approximately 2 atms, for 3.6 Kelvin this value is approximately 1.5 atms. For still lower temperature it is necessary to throttle to pressures which are even lower. This implies that the compressor will have to be of a very large size in a closed system and that the low-pressure sides of the heatexchangers must have a low resistance to flow. This renders the known machines complicated, bulky and expensive. Further, if an opened system is concerned, in which the high-pressure medium is derived from one source or other and the medium of reduced pressure after heat-exchange with the object to be cooled is led off to the surroundings, the machine cannot be self-blowing off if cold is to be produced at temperatures which correspond to a pressure below atmospheric pressure. Consequently steps will have to be taken for removing the medium of reduced pressure from the machine.

These machines have the further disadvantage that the pressure energy of the high-pressure medium is dissi- 3,442,093 Patented May 6, 1969 pated in the Joule-Kelvin cocks without further use, thus involving a loss.

The present invention relates to a machine for producing cold and/ or for liquefying gases in which the disadvantages of the known machines noted above are obviated. The new machine has at least one inlet for high-pressure medium which is connected to one or more heat-exchangers in which the high-pressure medium is cooled below the inversion temperature corresponding to this pressure. The machine also includes at least one ejector having a jet tube to which at least part of the cooled high-pressure medium may be supplied. The outlet of the ejector is connected, possibly through a first container for collecting medium of reduced pressure, (a) through one or more of the heat-exchangers to an outlet through which the medium of reduced pressure can leave the machine, (b) through one or more throttling devices and possibly a heat-exchanger to one or more further containers in which lower pressures prevail and which are connected to the suction side of the ejector.

An ejector is to be understood in connection with the present patent application to mean a device in which the potential energy of a high-pressure (primary) medium is changed wholly or in part to kinetic energy which is used, at least in part, for increasing the pressure of a second (secondary) medium.

In the machine to which the invention relates the energy of the highpressure medium supplied to the ejector is used, at least in part, to draw oli the vapour from the container of lower pressure, and to bring this vapour to the pressure which prevails in the system of conduits through which medium of reduced pressure is removed from the machine. The cold can now be delivered at a pressure which is lower than the pressure at the outlet. This affords the advantage that, in an open system, the machine can be self-blowing off and the cold is delivered at a pressure which is lower than the blowing-01f pressure. In a closed system which includes a compressor having its outlet connected to the inlet for high-pressure medium and its inlet connected to the outlet for medium of reduced pressure, the pressure ratio across the compressor can be considerably lower than is the: case in machines in which the high-pressure medium is reduced in pressure in Joule-Kelvin cocks.

In the machine to which the invention relates the pressure energy of the medium supplied to the ejector is not dissipated without further use, but it also utilized to pump up the vapour from the container of lower pressure to the suction pressure of the compressor or the pressure at which the medium leaves the machine again. The machine thus obtained has a higher efiiciency and a much more favourable pressure ratio in the heat-exchanger and across the compressor than is the case in machines in which Joule-Kelvin cocks are used.

The machine to which the invention relates is usable in particular when cold has to be delivered at very low temperatures. Especially of late, great: interest has been shown in cold delivered at temperatures lower than 4 Kelvin as used especially for cooling superconducting coils and computing or store elements of electronic computers. As previously mentioned, these low temperatures are accompanied by very low vapour pressures above the liquid bath in the container of lower pressure, which causes the object to be cooled. If it is desired for example, to deliver cold at 1 Kelvin, the corresponding vapour pressure in the container of lower pressure is 0.12 mm. Hg. A very satisfactory suction action of the ejector is required to maintain the said low pressure in the further container.

The invention underlies the recognition of the fact that, since the medium supplied to the ejector may have a temperature which is somewhat higher than that of the medium which leaves the ejector, a certain tempera ture gradient will occur across the ejector, resulting in thermal conduction, which detrimentally affects satisfactory operation of the ejector and especially the lowest suction pressure obtainable. An object of the invention is to provide a machine of the kind above referred to, whereby cold can be delivered with a higher efficiency and at lower temperatures than in known machines.

The machine according to the invention is character ized in regard to at least the jet tube of each ejector that at least those parts which contact the flow of medium during operation are made of a heat-insulating material. It is thus impossible for heat to be conducted through the walls of the jet tube towards the end of the jet tube, which is highly beneficial to satisfactory operation of the ejector. Not only the surface layer of the jet tube which contacts the medium flowing through it may be made of heat-insulating material, but it is also possible for the whole wall of the jet tube to be made of heatinsulating material. In another advantageous embodiment of the machine according to the invention all parts of the ejector, which during operation contact the flow of medium, are made of heat-insulating material. The heat-insulating material used in accordance with the invention may be glass or synthetic material or combinations thereof.

The invention also relates to an ejector suitable for use in a machine according to the invention, the ejector comprising a jet tube to which high-pressure medium may be supplied, a diffuser through which medium of reduced pressure can leave the ejector, and a suction side through which medium of lower pressure may he drawn in. This ejector is characterized in that those parts of the jet tube which contact the flow of medium during operation are made of a heat-insulating material.

In order that the invention may be readily carried into effect a preferred embodiment will now be described in detail, with reference to the accompanying diagrammatic drawings, in which:

FIGURE 1 shows a machine for producing cold in which an ejector is used (out of scale);

FIGURES 2 and 3 show, on a larger scale, two embodiments of the ejector used in the machine of FIGURE 1.

In FIGURE 1 reference numeral 1 indicates a compressor. The compressed medium first passes through a cooler 2 in which the heat of compression is dissipated, and then flows through a heat-exchanger 3 in which it exchanges heat with medium of a lower pressure. The high-pressure medium is then cooled in a heat-exchanger 4 to a temperature of, for example, 60 Kelvin by means of a cooling device 5. Next the high-pressure medium flows through a heat-exchanger 6 in which it again exchanges heat with medium of lower pressure, and is then cooled in a heat-exchanger 7 to a temperature of, for example, 15 Kelvin by means of a cooling device 8. Thereafter the high-pressure medium again changes heat with expanded medium in a heat-exchanger 9; the high-pressure medium then has a temperature which lies below the inversion temperature of this medium at the pressure prevailing. The medium subsequently enters an ejector 10 in which it is reduced in pressure. The ejector is connected to an outlet 11 which includes a container 12. The vapour space of container 12 is connected through the heat-exchangers 9, 6 and 3 to the inlet side of compressor 1. Condensate from container 12 can flow through a heat-exchanger 13 and a throttle cock 14, in which the liquid is further reduced in pressure, to a container 15 in which a pressure lower than that in container 12 prevails. The vapour space of container 15 communicates through heat-exchanger 13, with the suction side 16 of ejector 10.

A cooling coil 17 through which a medium to be cooled can flow is arranged in container 15. If desired, it is possible to replace this coil by an object to be cooled,

such as a superconductive coil or a computing or store element of an electronic computer. The medium used in this apparatus is helium.

Compressor 1 compresses helium to a pressure P1. This high-pressure medium is cooled in the heat-exchangers 2, 3, 4, 6, 7 and 9 below the inversion temperature corresponding to this high pressure of the medium. The highpressure medium is then supplied to ejector 10 in which it is reduced in pressure during which process the potential energy is converted in part into kinetic energy which in turn is used in part for bringing the low pressure medium to the required pressure. The medium which leaves the ejector at a pressure P2, is collected in container 12. The vapour at pressure P2 can then flow through the said heat-exchangers back to the compressor again. The liquid produced is throttled in a throttle device 14 to a pressure P3 which corresponds to the temperature at which the cold is to be delivered. The vapour at pressure P3 in container 15 is drawn off by the ejector 10 and brought to the pressure P2 of container 12. Before entering the ejector 10, the vapour from container 15 exchanges heat with medium of higher pressure in the heat-exchangers 13 and 18. In this machine the compressor thus operates between the pressures P2 and P1 so that this compressor may be much simpler in structural respect than in machines in which throttling takes place in Joule-Kelvin cocks where the compressor operates between the pressures P3 and P1.

FIGURE 1 shows, by way of example, one embodiment of a machine for producing cold Which utilises an ejector. Further embodiments are described in US. patent application, Ser. No. 511,044, filed Dec. 2, 1965.

FIGURE 2 shows an ejector 10 on a larger scale. The high-pressure medium leaves heat-exchanger 9 at a temperature of, for example, 4 Kelvin and is supplied at 20 to a jet tube portion 21 of the ejector. At the end of this jet tube portion the temperature of the medium will have decreased to a lower value, which implies that a temperature gradient decreasing from the inlet 20 to the outlet 22 of the jet tube also exists within the walls of the jet tube portion 21. Unless special steps are taken, heat would be conducted from the inlet to the outlet of the jet tube through the wall of the jet tube and this will, of course, detrimentally affect satisfactory operation of the ejector. To prevent this the jet tube 21 of the ejector shown in FIGURE 2 is internally covered with a layer of a heat-insulating material 23. Now substantially no heat will be conducted through the walls of the jet tube which is naturally beneficial to the operation of the ejector and more particularly to the lowest suction pressure obtainable.

Instead of manufacturing only the surface layer 23 of a heat-insulating material, it may be advantageous to make the entire jet tube portion 21 of insulating material, and it is even advantageous, as shown in FIGURE 3, to manufacture an ejector which wholly consists of a heatinsulating material, such as glass or a synthetic material. This considerably limits thermal conduction via the walls of the ejector, resulting in more satisfactory operation of the ejector and a lower suction pression obtainable.

It will be evident that, in order to obtain even more satisfactory operation of the ejector, steps may be taken to draw off the boundary layers formed on the walls of the jet tube and on the diffuser. Further, the ejector may be provided with a heating device arranged within or around the wall of the jet tube in order that, if fixed particles have deposited on the inner wall of the jet tube, these particles may be removed by slightly heating the jet tube.

I claim:

1. A cold producing apparatus for use with fluid medium from a high pressure source comprising: (a) at least one heat exchanger for cooling said high pressure medium to below the inversion temperature corresponding to its pressure, (b) at least one ejector having a jet tube part through which at least some of said cooled high pressure medium is supplied and expanded to a lower pressure, (c) a first reservoir for collecting said expanded medium at lower pressure, (d) a throttling device for further expanding the medium from the first reservoir, (e) a secand reservoir for collecting medium from said throttling device, said second reservoir having an outlet connected to the suction side of said ejector, and (f) and at least those parts of said jet tube which are contacted by medium during operation of the apparatus, are constituted of a heat insulating material.

2. A cold producing apparatus as claimed in claim 1 wherein parts of said ejector which contact the medium flowing therethrough during operation of the apparatus, are constituted of a heat insulating material.

3. A cold producing apparatus as claimed in claim 1 wherein each ejector is constituted of synthetic material.

4. An ejector for use in a cold producing apparatus, comprising: a jet tube through which high pressure medium is supplied, and a diffuser through which medium reduced in pressure can leave said ejector, the ejector including a suction inlet through which medium of low pressure may be drawn in, and at least those parts of said jet tube which are contacted by the medium flowing therethrough during operation of the ejector are constituted of a heating insulating material.

5. An ejector for use in a cold producing apparatus as claimed in claim 4 being constituted of glass.

6. A cold producing apparatus comprising a medium supply under high pressure and a temperature below the inversion temperature associated with said pressure, at least one ejector having a jet tube to which at least part of said high pressure medium can be supplied, at least one heat exchanger through which the outlet of said ejector communicates therewith, at least one pressure reducing device, said medium being reduced in pressure through said pressure reducing device, and the wall of said jet tube which is contacted by said medium being constituted of a heat insulating material.

References Cited UNITED STATES PATENTS 2,852,922 9/ 1958 Neumann 62-500 3,208,399 9/ 1965 Keller 103260 WILLIAM J. WYE, Primary Examiner.

US. Cl. X.R. 

